为了研究草本植物根系作用下浅层黄土强度的影响，本文设计了含紫花苜蓿根系黄
土抗剪强度的试验方案，考虑了低围压/垂直压力状态，人工培育了含根系黄土试样，通 过三轴试验、直剪试验和根系拉拔试验研究了含根系黄土的强度特性和根系抗拔特性； 然后通过根系拔出力对 WWM 
模型进行了优化；并研究了植被根系生长效应对含紫花 苜蓿根系黄土边坡稳定性的影响。本研究得出的主要结论如下：
（1）低围压状态下试样应力应变曲线为应变软化型，高围压状态下试样应力应变 曲线为应变硬化型。抗剪强度指标拟合结果表示，含根系土体的黏聚力要明显大于素土， 内摩擦角基本无明显变化。
（2）断裂处直径对拔出力没有影响，拔出长度和地表处直径都对拔出力有显著影 响。WWM 模型的修正系数 k″可以用一个与时间相关的函数表示，k″随时间增长呈现出 
先增大后减小的趋势，k″的减小趋势随生长时间单调减小。
（3）在滑面深度为 0~1m 的范围内，随着滑面深度的增大，边坡稳定系数始终呈现 出单调减小的趋势；随着边坡坡角的增大，边坡稳定系数呈现先减小后增大的趋势。通 
过理论值计算的边坡稳定系数要明显大于通过试验值计算的边坡稳定系数。
（4）植被的存在能够显著改善坡面的应力、位移和塑性区分布，这说明植被能够有
效地抑制降雨条件下坡面的浅层滑坡，植被增强坡面稳定性效果随着植被生长更加显著。

    In order to study the strength of shallow loess under the action of herb root, this paper designs the test scheme of shear strength of loess with alfalfa root, considers the state of low confining pressure / vertical pressure, and artificially cultivates loess samples with root through triaxial test The strength characteristics and root pullout resistance of loess with roots were studied by direct shear test and root pullout test; Then the WwM model was optimized by root pull-out force; The effect of vegetation root growth on the stability of loess slope with alfalfa root system was studied. The main conclusions of this study are as follows:
    (1) Under the condition of low confining pressure, the stress-strain curve of the sample is strain 
softening type, while under the condition of high confining pressure, the stress-strain curve of 
the sample is strain hardening type. The fitting results of shear strength index show that the cohesion of soil with roots is obviously greater than that of soil without roots, and the internal 
friction Angle has no obvious change.
    (2) The diameter of the fracture has no influence on the pull-out force, while the pull-out length and the diameter of the surface have significant influence on the pull-out force. The correction 
coefficient of the WWM model k″ can be expressed as a time-related function. With the growth of  time, k" firstly increases and then decreases, and the decreasing trend of k" decreases monotonically with the growth time.
    (3) When the sliding surface depth is 0~1m, the slope safety factor always shows a monotonically decreasing trend with the increase of the sliding surface depth. With the increase of the slope angle, the slope safety factor firstly decreases and then increases. The slope safety factor calculated by the theoretical value is obviously larger than that calculated by the test value.
(4) The existence of vegetation can significantly improve the distribution of slope  stress, displacement and plastic zone, which indicates that vegetation can effectively inhibit shallow slope landslide under rainfall conditions, and the effect of vegetation enhancing slope stability is more significant with the growth of vegetation.